Many manufacturing applications require the generation of a linear force for movement of machining equipment. Conventional A/C and D/C motors produce a rotary torque about an axis which must be converted into a linear force before it can be used in such applications. Such conversion is accomplished by a screw and nut, a sheave and cable, or a rack and pinion, among others. These designs are problematic in that they tend to wear out relatively quickly, and they are incapable of producing high linear speeds.
Linear motors are also known which directly produce a linear force in response to an electric input. Typically, a linear motor takes advantage of the variable magnetic reluctance produced in the vicinity of slots in a pole face of a magnetic member. An armature of a magnetic material, having windings therein, is urged to step from position to position along the pole face as defined by the slots or, alternatively, the magnetic member is movable while the armature is stationary.
In such designs, the armature portion usually comprises a coil disposed within a lamination stack, and surrounded by an epoxy block. A cooling tube is typically provided adjacent the epoxy block for drawing heat from the armature.
The force which such linear motors are capable of producing is limited by resistive heating in the windings of the armature of the motor. The normally used copper cooling tube requires mechanical retention within the epoxy case, and provides somewhat limited armature cooling capacity. Accordingly, it is desirable to provide an improved armature design with increased cooling capacity.
Another problem with such designs is that the epoxy molding may create difficulty in manufacturing the armature. The epoxy is typically molded around the coil and laminate stack within a separate mold. It is then removed from the mold and trimmed, and the mold is cleaned out for the next molding operation. These steps require handling which adds manufacturing cost. Additionally, the wire harness typically gets wet and is subject to damage during epoxy molding and grinding of the epoxy block.
Another shortcoming of prior art designs is that wire harnesses extending from the epoxy block are typically unprotected and exposed to damage or moisture during operation of the linear motor. Wire harness damage may result in substantial downtime for the equipment.
A further shortcoming of prior art designs is that such designs are typically limited to a single-pass cooling arrangement wherein a cooling fluid travels from one end of the armature to another. In this configuration, the cooling fluid may be substantially heated by the time it reaches the opposing end of the armature, and therefore uneven cooling occurs.